Systems and methods for comparing documents containing graphic elements

ABSTRACT

A system and methods for comparing a plurality of documents comprising graphic elements is described. Attributes of graphic elements amongst the documents are examined to identify sufficiently similar graphic elements. A merged document can be automatically produced based on the comparison. Graphic elements in the resulting document may be associated with a document layer. Methods may advantageously be applied to a plurality of documents representing different versions of a document.

REFERENCE TO RELATED APPLICATION

This application is a continuation in part of U.S. patent applicationSer. No. 11/114,078 entitled “Systems and methods for comparingdocuments containing graphic elements”, filed 26 Apr. 2005 which ishereby incorporated by reference herein.

TECHNICAL FIELD

This invention relates to comparing documents comprised of graphicelements to identify similarities and/or differences between thedocuments being compared. Some embodiments of the invention facilitatemerging graphic elements from documents.

BACKGROUND

Document creation and production (e.g. printing) often involves makingchanges to a document. The changes may result from iteration in thecontent creation phase, corrections identified after the contentcreation phase or requirements of the production phase. Inevitably,different versions of a document result. Persons working with differentversions of documents desire tools for identifying differences betweenversions. In some circumstances, there is a desire to merge some contentfrom one version of a document with other content from another versionof the document.

Microsoft® Word® 2003 software includes features capable of identifyingdifferences between documents consisting primarily of textual content.For example, two documents, having some common textual content, can becompared to identify components common and unique to each document.Furthermore, one document can be merged with the other, based oninformation obtained during the comparison.

In the graphic arts field however, documents often comprise contentincluding combinations of text, photographic images and artwork.

Microsoft® Word® 2003 provides only limited support for comparing andmerging non text elements. For example, a Microsoft® Word® 2003 documentcontaining a combination of text, inserted images and artwork (drawnwith the integrated drawing function provided by Microsoft® Word® 2003)can be compared. The comparison does not recognize changes that involvesubstituting an inserted image file with a file having a differentfilename corresponding to a modified form of the original image.Similarly, the comparison does not recognize certain changes in thedrawn artwork (e.g. changing the dimensions of a drawn rectangle). Otherchanges in artwork, such as changing the fill color of a drawn rectanglecause the entire drawing frame to be recognized as different during acomparison.

Other document creation software, such as Adobe® FrameMaker® 7.0exhibits similar behavior. The user documentation for Adobe® FrameMaker®7.0 indicates that artwork objects placed in an anchored frame, withinthe text flow of an Adobe® FrameMaker® 7.0 document, are compared. Ifthe objects are different, or if they are in different positions (forexample, if they have a different front to back order), the entireanchored frame is marked as changed. Experimentation reveals that somechanges to objects, such as resizing, are not recognized during acomparison. Similarly, changes to artwork inserted as an encapsulatedPostScript® (.eps) file, are not recognized during a comparison.

Document interchange formats can represent documents having mixedcontent. Some document interchange formats, such as TIFF and CT/LW,normalize content as raster pixels. An advantage of this format is thatconversion to a production format is relatively simple, since mostdisplay and printing devices are raster oriented. A disadvantage of thisformat is that information about the structure of the content is lostduring the rendering process that produces raster pixels.

There exist software tools for comparing raster documents. Such toolsmay compare raster pixels to determine differences. Typically, thesedifferences are displayed visually by highlighting individual pixels ina contrast color or by highlighting a region surrounding any changedpixels. Merging two raster documents can be accomplished by manuallyselecting pixels from each document. This is not practical wheresignificant differences occur. Automation is also difficult since thereis little context information upon which to determine the document toselect for each pixel. An example of a tool that compares raster imagesis Artwork Systems ArtPro 6.5™, which provides an “export differences”function that operates to compare two jobs. When calculating thedifferences, ArtPro scans the job in pixels, it does not look at vectorinformation.

Other document interchange formats, such as Adobe® PostScript® andAdobe® Portable Document Format (PDF), represent content as vectorelements. A document comprises page description language statements thatdefine vector based graphic elements (e.g. text, images and symbolclipping paths). The language describes elements with attributesidentifying their characteristics and their layout on a page. Thelanguage also describes the order in which each element is to bedisplayed on a page. In this context, vector format has advantages anddisadvantages opposite those of raster format.

Adobe® Acrobat® provides a document comparison function with threelevels of analysis detail. Experiments, using PDF files created byprinting from modified versions of an Adobe® Illustrator® documentsuggest that pixel comparison is being performed. For example, comparingwith the most detailed level of analysis, Acrobat® can detect a singlepixel variation in an imported image. This is highlighted visually as apath surrounding the vicinity of any changed pixels. Similarly, changesmade to a PDF file using a PDF editor application (e.g. EnfocusPitstop™) to increase the size of a path graphic element (e.g. atriangle shape) are detected by Acrobat® and visually highlighted aschanges in a small portion of the boundary of the path graphic element.The entire path graphic element is not highlighted as having beenchanged.

Enfocus Pitstop™ allows a user that is editing graphic elements in a PDFdocument to identify differences based on session logs that track editsmade to graphic elements within that document.

Creo® Seps2Comp™ software examines attributes of graphic elements frommultiple pages of a single document. Each page of the documentrepresents a different printing colorant, generated from a compositecolor document during the step of creating the document interchangeformat. Seps2Comp examines attributes of graphic elements to infer thecomposite graphic element based on similarity between attributes of thecolor separated graphic elements. Similar elements from separate pagescan be composited by combining their colorants and tonalities fromseparate pages into a single graphic element on a single page. Seps2Componly operates in an automated fashion. In some situations, it caninappropriately declare graphic elements as being similar or different.The algorithms and rules for determining similarity are not ideal and nomethod for compensating for mistakes exists.

Thus, there remains a need for effective systems and methods forcomparing documents containing a variety of types of elements. Printingof packaging materials is one field where the needs are acute. Twofactors exacerbate the acuteness. First, packaging documents are oftenproduced with variations to suit needs of different regions or markets.The variations are usually included in the original native documentformat and may be manifested as separate layers that can be selectivelyenabled prior to producing the document interchange format for aspecific region or market. Thus, a number of different documents may beprinted from each original document. The multiple documents can includea significant number of common graphic elements.

Second, during the print production phase, a packaging converter willinvest significant time and skill in preparing a document for printing.This can include trap processing, which adds graphic elements, atboundaries between graphic elements to improve the quality of theprinted material. It can also include halftone screen assignment, whichspecifies the nature of the rendered pixels, on a graphic element basis,to improve the quality of the printed material. It can also includeediting the graphic elements to make corrections in content, such asfixing spelling mistakes. Other print production processing activitiescan also occur.

Packaging converters, faced with two or more significantly commondocuments, cannot afford to absorb the significant costs associated withduplicating production activities to account for regional variations andlast minute content changes. Furthermore, the process for producingprinting plates is time consuming and packaging converters require toolsfor visualizing the differences between documents prior to makingplates. Visualizing differences at the graphic element level, instead ofthe pixel level, is important. In many cases, regional variations orcontent changes affect only specific plates corresponding to specificcolors (usually black and spot colors).

The foregoing examples of the related art and limitations relatedthereto are intended to be illustrative and not exclusive. Otherlimitations of the related art will become apparent to those of skill inthe art upon a reading of the specification and a study of the drawings.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods which aremeant to be exemplary and illustrative, not limiting in scope. Invarious embodiments, one or more of the above-described problems havebeen reduced or eliminated, while other embodiments are directed toother improvements.

This invention provides systems and methods for comparing documents.Preferred embodiments compare vector format documents such as documentsconformant with the Adobe® Portable Document Format (PDF) specification.A system according to one embodiment of the invention includes an Adobe®Acrobat® plug in software module that comprises a document comparatorand a document merger. The Document Comparator examines attributes ofselected graphic elements in a first document and a second document togenerate an edit script that identifies graphic elements that would needto be deleted from the first document and graphic elements that wouldneed to be added to the first document to make the first document likethe second document. The selected graphic elements may correspond tographic elements created during the content creation phase.

Examined graphic elements may be compared using rules that allow graphicelements with only minor differences in attribute values to beidentified as equivalent. The Document Merger applies the edit script tothe first document to produce a merged document that is similar to thesecond document. Applying the edit script causes deletion of graphicelements unique to the first document and addition of graphic elementsunique to the second document. Because of the selection criteria andrules applied by the Document Comparator, graphic elements from thefirst document that are sufficiently similar to those in the seconddocument may be preserved. Graphic elements from the first document thatwere not selected for comparison can also be preserved. Preservation ofgraphic elements is particularly advantageous when those graphicelements were affected by significant investment of time and skillduring a production phase.

An optional Comparison Visualizer applies portions of the edit script,in conjunction with the first and second documents, to produce a layeredview with each layer showing certain graphic elements. One exemplarylayered view presents graphic elements in three layers. One layercontains graphic elements common to both documents. Another layercontains graphic elements unique to the first document. A third layercontains graphic elements unique to the second document. Controls areprovided to alter the visual appearance of identified graphic elementsto facilitate visualization of similarities and differences amongstgraphic elements. The Comparison Visualizer also provides controls toselect one or more graphic elements and override the actions,corresponding to the selected graphic elements, in the edit script.

Thus, user defined modifications of the automatically generated editscript can be made and the modified edit script re applied to produce adesired merged document result. Optional Additional Document Processingcomponents examine graphic elements in the merged document to performadditional processing. As an example, a trap processing engine processesthe merged document to adjust trap graphic elements preserved from thefirst document and add trap graphic elements. Both may be required bythe addition of graphic elements from the second document.

These and other aspects of the invention and features of embodiments ofthe invention are illustrated in greater detail in the detaileddescription.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thedrawings and by study of the following detailed descriptions.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be considered illustrative rather than restrictive.

In drawings which illustrate non limiting embodiments of the invention:

FIG. 1 is a schematic diagram representing a computer system environmentaccording to one embodiment of the invention;

FIG. 2 is a block diagram illustrating the functional components of asystem according to one embodiment of the invention;

FIG. 3 is a flow chart diagram illustrating a method for processingdocuments according to one embodiment of the invention;

FIG. 4 is a flow chart diagram illustrating a method for comparinggraphic elements amongst two documents to produce an edit script capableof merging the documents;

FIG. 5 is a diagram illustrating the rendered appearance of a firstdocument, after content creation;

FIG. 6 is a diagram illustrating the rendered appearance of a firstdocument, after initial production processing;

FIG. 7 is a data structure diagram illustrating the documentcorresponding to FIG. 6;

FIG. 8 is a diagram illustrating the rendered appearance of a seconddocument, created by revising content of a first document;

FIG. 9 is a data structure diagram illustrating the documentcorresponding to FIG. 8;

FIG. 10 is a data structure diagram illustrating an edit script capableof merging a second document into a first document;

FIG. 11 is a diagram illustrating the rendered appearance of a mergeddocument created by applying an edit script to a first document;

FIG. 12 is a data structure diagram illustrating the documentcorresponding to FIG. 11;

FIG. 13 is a diagram illustrating the rendered appearance of a documentcreated by performing additional processing on a merged document;

FIG. 14 is a data structure diagram illustrating the documentcorresponding to FIG. 13;

FIG. 15 is a diagram illustrating a portion of a GUI that presents alayered view of graphic elements, with those being common to bothdocuments prominently displayed;

FIG. 16 is a diagram illustrating a portion of a GUI that presents alayered view of graphic elements, with those being unique to the firstdocument prominently displayed;

FIG. 17 is a diagram illustrating a portion of a GUI that presents alayered view of graphic elements, with those being unique to the seconddocument prominently displayed;

FIG. 18 is a diagram illustrating graphic elements of an exemplary setof version documents according to one embodiment of the invention;

FIG. 19 is a diagram illustrating an exemplary method for mergingversion documents into a layered document according to one embodiment ofthe invention; and

FIG. 20 is a diagram illustrating intermediate results of an exemplaryversion document merging method according to one embodiment of theinvention.

DESCRIPTION

Throughout the following description, specific details are set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well known elements have not been shown or described indetail to avoid unnecessarily obscuring the invention. Accordingly, thespecification and drawings are to be regarded in an illustrative, ratherthan a restrictive, sense.

FIG. 1 is a schematic diagram of a computer system 100 according to anembodiment of the invention. Computer system 100 has a processing unit112 that operates a software embodiment of the invention. Processingunit 112 has access to data store 110 providing temporary and permanentstorage of data. Data store 110 can be part of computer system 100 orcan be provided in another computer system accessible to processing unit112. Processing unit 112 has a user interface comprising one or moreinput devices and output devices. For example, output devices caninclude a graphical monitor 114 suitable for presentation of a GUI, andinput devices can include a mouse 116 and a keyboard 118.

The remainder of the description describes operation of embodiments ofthe invention by illustrating:

-   -   A method for automatically comparing a first document and a        second document to produce a merged document while preserving        production phase investment in graphic elements of the first        document;    -   A method for automatically determining graphic element        similarity and an edit script consistent with the merging method        above;    -   An example illustrating the methods above; and    -   Methods for visually comparing the common and unique graphic        elements among two documents that also allow a user to modify an        edit script consistent with the merging method above.

FIG. 2 is a block diagram illustrating the functional components ofcomputer system 100 according to an embodiment of the invention. A firstdocument 201 comprises page description data, which defines the layoutof one or more pages to be printed using a page description language.The page description data defines graphic elements such as text, images,and artwork (e.g. paths, shadings and blends). Graphic elements haveattributes that relate to their visual appearance (e.g. clipping path,stroke, fill, and font type). A second document 202 is similarlyconstructed. For illustrative purposes, a contrived history of examplefirst and second documents is outlined below.

In this example, documents 201 and 202 have a common origin, having beenproduced during a first content creation phase by an artist, whose goalwas to produce a particular visual intent. Graphic elements definedduring a content creation phase are considered “content graphicelements”. First document 201 was modified during a first productionphase, following the first content creation phase. The purpose of themodifications was to improve the quality of the printed result or tofacilitate some production process. During the production phase, graphicelement attributes in first document 201 were modified (e.g. halftonescreens were assigned or modified). Trap graphic elements were alsoadded to first document 201 during the production phase. Theseproduction phase activities involved some labor intensive activities.Graphic elements, such as trap graphic elements, added during theproduction phase are considered “production graphic elements”. Graphicelement attributes modified during the production phase are consideredproduction modified graphic element attributes. First document 201 wasready to print from a production perspective. However, the content offirst document 201 is no longer suitable to print.

Second document 202 was created during a second content creation phasethat involved making revisions to first document 201 to reflect new orchanged content. The revised content can include corrections or changesin artistic intent. Regardless, a second production phase begins,corresponding to processing of second document 202, which has the goalof printing second document 202 while preserving as much firstproduction phase investment in first document 201 as possible.Investment in the production phase of first document 201 can bepreserved where it is independent of content revised in second document202.

According to one embodiment of the invention, documents are PDFdocuments produced, for example, by printing from a document creationapplication using Adobe®PDF Writer. In such an embodiment, some or allof the processing parts of system 200 can be encapsulated as softwareplug ins compatible with Adobe® Acrobat® software. For illustrativepurposes, the remainder of this description is based on PDF documentsand Adobe® Acrobat® plug in architecture. Other embodiments can includeother software architecture models and document formats. Alternativedocument formats are compatible with the invention if the documentformat can be interpreted to form a display ordered list of graphicelements.

“Display ordered” means that, when rendered by an image processor, thedocument's graphic elements are displayed in a specified order. Displayordering is important when graphic elements overlap with one another.Image processors can choose to display later ordered graphic elementsusing a knockout or overprint technique. A knockout technique results ina later ordered graphic element obscuring earlier ordered graphicelements in regions where they overlap. An overprint technique resultsin colorants from overlapping graphic elements combining in regionswhere they overlap. The resultant combination can depend, at least inpart, on the relative ordering of the contributing graphic elements.Documents referenced in FIG. 2 can exist as files in data store 110 orcan exist as data streams or other formats compatible with processingunit 112.

FIG. 3 is a flow chart diagram describing a basic method for processinggraphic documents according to a preferred embodiment of system 200. Themethod begins at block 302 with a user interacting with a GUI providedby document comparator 210 via input devices 116 or 118 and monitor 114.

Some preliminary production phase processing, known as refining, canoccur at or prior to the start of the method so that equivalent graphicelements are consistently defined in the two documents. As an example, aproduction facility can convert a content phase document to the PDFformat from some other page definition format (e.g. native documentcreation format or PostScript® format). In addition, the syntax and/orthe semantics of the page description data may have been altered. Syntaxchanges can involve representing a document utilizing a differentversion of the page description language having desirable features.Semantic changes, manifested as changes to graphic elements and theirattributes, can correspond with adopting production policies (e.g.always overprint, re sampling images to a specific resolution,converting filled path graphic elements into separate stroke and fillpath graphic elements).

In block 304, document comparator 210 interprets the page descriptiondata from first document 201 and second document 202 to produce displayordered graphic element list (display list) versions of each of thedocuments. Methods for interpreting page description data into a displaylist are well known in the art. Unless otherwise specified below,subsequent references to first document 201 and second document 202pertain to the display list versions of those documents.

In block 306, document comparator 210 examines selected (see below)graphic elements defined by first document 201 and second document 202to produce an edit script 250 that that is capable of producing mergeddocument 203 which is similar in appearance to second document 202 butpreserves some graphic elements from first document 201. Otherembodiments of the invention can include edit data in other forms thatcan be utilized to provide a similar result to edit script 250.

The method continues at 308, document merger 220 applies edit script 250to first document 201. One result is merged document 203, with graphicelements not selected for comparison and those identified as similar inthe two documents preserved from first document 201. Further, graphicelements unique to first document 201 are deleted, and graphic elementsunique to second document 202 are added, preserving their relative orderfrom second document 202. Document merger 220 can set attributes onpreserved graphic elements indicating the need to re examine anyproduction modified attributes.

Document merger 220 also examines production graphic elements present infirst document 201 to determine whether to delete them. Rules can beestablished to govern this, based on edit script 250 and otherinformation. As an example, trap graphic elements are deleted from firstdocument 201 if either of the content graphic elements referenced by thetrap graphic element are deleted, since the boundary between thesegraphic elements no longer exists. Conversely, a trap graphic element ispreserved in first document 201 if both of its referenced graphicelements are preserved. Other types of production graphic elements andother scenarios can be accommodated utilizing additional or differentrules.

Block 308 completes with document merger 220 producing merge report 204,comprising information about graphic elements affected by the mergeprocess. Information in merge report 204 can include summary or detailinformation about graphic elements affected by the merge or can identifyimpacts to the production process corresponding to the affected graphicelements. For example, merge report 204 can identify which printingcolorants are unaffected by the merge, so that previously-createdprinting plates corresponding to one or more colorants can be reused.Merge report 204 can be saved in data store 110 or can be presented in aGUI via monitor 114.

Proceeding at block 309, a decision is made whether to perform a visualcomparison of the documents. This can be based on a user preference orin response to a query provided in document merger 220 GUI. If thedecision is yes, a visual comparison is performed starting with block310 as described below. If the decision is no, the method continues atblock 318.

Proceeding at block 318, a decision to perform additional processing ismade. This can be based on a user preference or in response to a queryprovided in document merger 220 GUI. Additional document processing 240provides this processing. If the decision is no, block 322 is performedwherein document merger 220 converts merged document 203 into its pagedescription data format suitable for use by other productionapplications. Document merger 220 can save merged document 203 to datastore 110 and/or can keep it available in processing unit 112 for use byother applications.

If the decision at block 318 is yes, block 320 is performed. Additionaldocument processing 240 can include trap processing or any otherprocessing relevant to the production phase. In one embodiment of theinvention, additional document processing 240 includes two additionaltrap processing steps. First, preserved trap graphic elements are reexamined to determine whether any added or deleted graphic elementsaffect the clipping path of the preserved trap graphic elements. As anexample, an added graphic element, situated adjacent to or overlapping atrap graphic element, can cause trapping rules, stored in associationwith the preserved trap graphic elements, to clip part of the trapgraphic element along the path of the added graphic. In general,trapping rules can be quite complex and thus a variety of changes to oneor more existing trap graphic elements can result from an added graphicelement. Second, trapping rules can be applied to any added contentgraphic elements where these elements become adjacent to or overlapother content graphic elements in merged document 203. Additionalprocessing 240 produces processed merged document 205 from mergeddocument 203.

Additional document processing 240 next updates or produces anadditional merge report 204 that provides information about the trapprocessing and its effects on graphic elements. Next, at block 322,additional document processing 240 converts processed merged document205 into its page description data format and saves it to data store110.

Automatic Edit Script Creation

FIG. 4 is a flow chart diagram describing a method that may be used bydocument comparator 210 to produce edit script 250. The method starts inblock 402 with a first goal of producing two ordered lists of uniqueidentifiers corresponding to the selected graphic elements in firstdocument 201 and second document 202, respectively. The identifiers areunique amongst the graphic elements defined by both documents. Accordingto the invention, and described in detail below, a graphic element issimilar to another graphic element (i.e. they have the same identifier),if compared attributes are similar, within defined accuracy, to thecorresponding attributes of the other graphic element.

The method proceeds at block 404 by selecting first document 201 as thecurrent document. Next, block 406 identifies the first graphic elementto be displayed by the current document as the current graphic element.

Proceeding at block 408, the graphic element selection criteria areapplied. According to one embodiment of the invention, selectioncriteria identify only content graphic elements, consistent with thegoal of preserving production phase investment in first document 201. Asan example, corresponding to the method of FIG. 4, trap and otherproduction graphic elements can be generated with an attributeidentifying them as production graphic elements. The selection criteriathus comprises testing for the absence of the production graphic elementattribute. Other criteria, based on this or combinations of otherattributes associated with the graphic elements can be established toidentify other categories of graphic elements. As an example, a criteriathat selects all graphic elements can be used to determine differencesbetween both content and production graphic elements in documents thathave both been subjected to production phase processing.

At block 408, if the current graphic element is not content, the methodproceeds to block 424. Otherwise, the method proceeds to block 410.

In the illustrated embodiment, comparisons between graphic elements arefacilitated by computing a hash value from attributes of the graphicelements. Other comparison methods may be used in other embodiments ofthe invention. In block 410 selected attributes of the current graphicelement are processed using a hashing algorithm. The hashing algorithmtakes variable-length data, corresponding to selected graphic elementattributes, and derives fixed-length data, or a hash value from thevariable-length data. The attributes and hashing algorithm are chosen sothat graphic elements having some similarities produce the same hashvalue.

Next, in block 412, the set of previously hashed graphic elements isexamined. If there is no hash list, identified by a hash valuecorresponding to the hash value of the current graphic element, a newhash list is created in association with the current graphic element andthe method proceeds to block 418 where the current graphic element isassociated with the next unique identifier. As an optimization, whenprocessing graphic elements from the first document, the method canalways proceed to block 418 since one can assume that each graphicelement in the first document is unique.

Otherwise, the method proceeds to block 414 where the current graphicelement is associated with an existing hash list identified by thecurrent graphic element's hash value. Next, a detailed comparison of thecurrent graphic element's attributes is performed with each graphicelement, associated with the hash list, to determine if any aresufficiently similar to be considered equivalent to one another.

Rules define the meaning of “sufficiently similar”. Tables 1 5 exemplifyrules according to a preferred embodiment of the invention. These rulesaim to ignore visually imperceptible differences between similar graphicelements. Other types of rules, involving graphic element attributes andother criteria, can also be utilized in accordance with the invention.For example, a rule can be established to ensure that a graphic elementselected from a document cannot be sufficiently similar to anothergraphic element from the same document. If two graphic elements from thesame document are otherwise sufficiently similar this can be brought tothe attention of the user as an unexpected result. Some embodiments ofthe invention permit a user to fine tune the rules for evaluating theequivalence of graphic elements or to select between different groups ofrules for evaluating the equivalence of graphic elements. TABLE 1Example Path Graphic Element Similarity Rules Attribute AccuracyClipping path control points 0.06 pts Painted colorants 0.01 Controlpoints (default user space) 0.06 pts Paint operation Equivalent Strokewidth (if and only if{iff} 0.06 pts stroked) Line join (iff stroked)Equal Miter limit (iff stroked) .1% of min scale Line cap (iff stroked)Equal Dash pattern (iff stroked) 0.06 pts

TABLE 2 Blend Graphic Element Similarity Rules Attribute AccuracyClipping path control points 0.06 pts Number of path elements Equal

TABLE 3 Shading Graphic Element Similarity Rules Attribute AccuracyClipping path control points 0.06 pts Shading dictionary Equal CTM deltatransform .1% of min scale CTM offset 0.03 pts

TABLE 4 Example Text String Graphic Element Similarity Rules AttributeAccuracy Clipping path control points 0.06 pts Painted colorants 0.001TRM delta transform .1% of min scale TRM offset 0.06 pts Text rendermode Equivalent PostScript ® font name Equal Word spacing 1.5 × 10 − 5Character spacing 1.5 × 10 − 5 String Equal Line width (iff stroked)0.03 pts Line (iff stroked) Equal Miter limit (iff stroked) .1% of minvalue Line cap (iff stroked) Equal Dash pattern (iff stroked) 0.03 ptsSub-paths Recursive application of path comparison

TABLE 5 Example Image Graphic Element Similarity Rules AttributeAccuracy Clipping path control points 0.06 pts Colorants Equal CTM deltatransform .1% of min scale CTM offset 0.03 pts Dimension Equal Bit depthEqual Pixel values Equal Mask type Equal Color mask (iff color masked)Equal Image mask (iff masked by Recursive application of image position)comparison

The single hash key method described above is suitable for attributeshaving discrete values. For attributes that have continuous (or asufficiently large number of) values, it can be advantageous to quantizea value range into discrete bins so that a discrete hashing algorithmcan be used. Depending on the degree of quantization and the tolerancesdefined by corresponding similarity rules, two graphic elements whichare sufficiently similar that they should be found to be equivalentcould produce different hash values using the single hash key method. Toensure that sufficiently similar elements, having these type ofattributes, are identified, multiple hash values can be generated foreach graphic element, based on the quantization and tolerance applied. Agraphic element could thus be associated with more than one hash list.When searching for sufficiently similar graphic elements, multiple hashlists, corresponding to multiple hash values generated for a graphicelement, are examined.

In a simplified example, assume that a hash value for a graphic elementof the “text” type is based only on a point size attribute. Furtherassume that point sizes are quantized, prior to hashing, into binnumbers corresponding to point sizes from 0 to 100 in increments of 0.1points. Further assume that text elements having point sizes within 0.06points are “sufficiently similar” for a particular application. If atext element has a point size of 10.05, rules dictate that it is similarto other text elements whose point size values are within the range(9.99<=size<=10.11). A first hash value is generated using a first bincorresponding to the range (10.00<=size<10.10) since the text element'spoint size (10.05) lies within that range. A second hash value isgenerated using a second bin corresponding to the range(9.90<=size<10.00) since a similar text element with point size (9.99)would lie within that range. A third hash value is generated using athird bin corresponding to the range (10.00<=size<10.10) since a similartext element with point size (10.11) would like within that range. Ifmultiple attributes requiring quantization were hashed, the number ofgenerated hash values would increase according to the number ofcombinations of potentially matching bins.

The method continues at block 416 where the result of the sufficientsimilarity comparison is decided. If the current graphic element is notfound to be sufficiently similar to any previously-processed graphicelements, the method proceeds to block 418 where the current graphicelement is associated with the next unique identifier. Otherwise, atblock 420, the current graphic element is associated with the uniqueidentifier associated with the graphic element that it is sufficientlysimilar to.

Proceeding from block 418 or 420 to block 422, the method appends thecurrent graphic element's identifier to the list corresponding to thecurrent document. A list of graphic element identifiers is preferred toa list of graphic elements because such a list utilizes fewer resourcesfrom processing unit 112 during later comparisons.

Proceeding to block 424, the method examines the current document todetermine if another graphic element exists after the current graphicelement. At block 426, if a next graphic element is found, it isidentified as the current graphic element and the method proceeds toblock 408. Otherwise the current graphic element is the last graphicelement in the current document. In the latter case, the method proceedsto block 428 where the current document is examined to determine if itis first document 201. If yes, second document 202 is identified as thecurrent document at block 430 and the method proceeds to block 406.Otherwise, the method proceeds to block 432, the first goal having beenaccomplished.

At block 432, the two lists are examined by document comparator 210 togenerate an edit script 250 capable of changing the first list into thesecond list. Specifically, edit script 250 comprises a set of graphicelement actions, including: delete (from first document 201), and add(from second document 202). Finally, document comparator 210 setsattributes of certain graphic elements to indicate that these graphicelements may require additional processing.

Methods suitable for creating edit script 250 are well known in the art.An example method proceeds by:

-   -   Examining items in both lists, in order, until a common item is        found.    -   Then, delete all items in the first list between the last common        item (or start of list initially) and the new common item.    -   Then, add all items that are unique to the second list, between        the last common item (or start of list initially) and the new        common item. Add them to the first list between the last and new        common item, preserving their relative order in the second list.    -   Repeat until both lists have been exhausted, treating the ends        of the lists as a common item.

An exemplary method, according to a preferred embodiment of theinvention, uses the so called “Largest Common Substring” algorithmdescribed by W. Miller & E. W. Meyers and detailed in “A File ComparisonProgram”, Software Practice and Experience 15(11), November 1985, pp.1025 1040. Other potential sources of related subject matter include:“The String to String Correction Problem with Block Moves”, ACMTransactions on Computer Systems 2(4), November 1984, pp. 309 321; “ATechnique for Isolating Differences Between Files”, Communications ofthe ACM 21(4), April 1978, pp. 264 268.

DETAILED EXAMPLE

This section details a simple example, further illustrating the methodsidentified in the foregoing description. FIG. 5 is a diagramillustrating a rendering of an exemplary first document 201, immediatelyfollowing the initial content creation phase. At this stage, firstdocument 201 comprises the following graphic elements, in display order:

-   -   Image 501    -   Rectangular path 510, having no stroke and a dark colored fill        having a clipping path CP1;    -   Triangular path 520, having no stroke and a light colored fill;    -   Square path 540, having no stroke and a dark colored fill;    -   Rectangular path 550, having no stroke and a light colored fill;    -   Rectangular path 560, having a medium width, dark colored stroke        and no fill, initially part of rectangular path 550 but        separated by a refining process; and    -   Text string 570, having no stroke and a dark colored fill.        Each graphic element has been assigned a default halftone screen        S1.

FIG. 6 is a diagram illustrating a rendering of exemplary first document201 shown in FIG. 5, immediately following the initial production phasethat included trap processing and halftone screening adjustments. FIG. 7is a data structure diagram corresponding to FIG. 6 and illustratingaspects of exemplary first document 201 and associated data.

Graphic element identifiers, shown in column 704, that would be createdaccording to the methods of FIG. 4, correspond to graphic elementreferences in FIG. 6. For illustrative purposes, the identifiers arechosen so that the last two digits indicate relative display order. Thehigher order digits reflect the number of the figure in which thegraphic element is first illustrated. This convention is continuedthroughout subsequent figures.

Trap graphic elements 611, 612, 621, 655 and 665A D have been addedduring the production phase to improve the printed quality at boundariesbetween light colored and dark colored content graphic elements. For thepurposes of illustration only, a trap graphic element is displayed afterthe darker content graphic element and before the lighter contentgraphic element. Further, a trap graphic element's clipping path isadjacent to the lighter colored graphic element and extends into thedarker colored graphic element. A trap graphic element is created as apath graphic element with a medium colored fill and no stroke.

FIG. 7 describes selected attributes of content and production graphicelements. Items of note include:

-   -   Hash values that would result from a comparison of graphic        elements according to the method described in FIG. 4 are shown        in column 706.    -   Attribute values, such as Clipping Path and Stroke Width, that        are pertinent to the example, are shown in column 708.

FIG. 7 describes selected production modified graphic attributes incolumn 710, reflecting:

-   -   the identification of production graphic elements,    -   the relationship between trap and content graphic elements, and    -   the halftone screen adjustments made (namely element 420 has        been associated with screen S2).

FIG. 8 is a diagram illustrating a rendering of an exemplary seconddocument 202, immediately following a subsequent content creation phasethat has occurred in parallel with the initial production phase. FIG. 9is a data structure diagram corresponding to FIG. 8 at this stage.Content revisions are highlighted in FIG. 9. In particular:

-   -   Image 501 has been deleted and thus is not shown in FIG. 9.    -   Rectangular path 802 and rectangular path 830 have been added.    -   Rectangular path 510 has been modified to have a new clipping        path, CP1A. Note that this modified graphic element, according        to the method of FIG. 4, would have the same hash value as        rectangular path 510 but upon detailed examination would not be        sufficiently similar and is thus assigned identifier 810.    -   Triangular path 520 has halftone screen S1 associated with it,        consistent with the original content phase definition.    -   Rectangular path 560 has been modified to have a wide stroke        width and is identified as 860.

FIG. 10 is a data structure diagram illustrating application of anexemplary edit script 250, generated using the method described in FIG.4 with inputs: first document 201, illustrated in FIGS. 6 and 7; andsecond document 202, illustrated in FIGS. 8 and 9. The ordered steps,shown in column 1002, include major steps, indicated by numerals,corresponding to edits that terminate with the preservation of a commonitem. Step actions, shown in column 1004, include:

-   -   “Delete”, corresponding to a content graphic element unique to        first document 201.    -   “Add”, corresponding to a content graphic element unique to        second document 202.    -   “No action”, corresponding to a graphic element identified as        sufficiently similar amongst both documents. In one embodiment        of the invention, this action can be included in the edit script        to enable generation of other types of documents using edit        script 250 as described below. Other methods for keeping track        of compared graphic elements that are sufficiently similar can        also be utilized.    -   “N/A”, corresponding to a graphic element that was not examined        during the comparison and thus is preserved in the merged        document. This action is not explicitly included in edit script        250.    -   “Derived delete”, corresponding to a production graphic element        depending upon one or more deleted graphic elements. This action        is not explicitly included in edit script 250 but is derived by        being related to graphic elements that were explicitly deleted.

Step parameters, shown in column 1006, identify the reference document(column 910) for the action and the relative add location (column 1012)where applicable. Additional processing attributes (column 1014)exemplify attributes set by document merger 220, includingidentification of new objects that may require trap processing andpreserved trap graphic elements that may require adjustment. Additionalprocessing outcomes (column 1020) indicate what would occur ifadditional processing is performed. Outcomes are described in moredetail in FIG. 13.

FIG. 11 is a diagram illustrating a rendering of exemplary mergeddocument 203. FIG. 12 is a data structure diagram corresponding to FIG.11, and illustrating aspects of exemplary merged document 203 andassociated data. Items of note include:

-   -   Graphic elements 501, 510, 611, 612, 655, and 560 were deleted        from first document 201 illustrated in FIG. 7 and thus are not        part of these figures.    -   Graphic elements 802, 810, 830 and 860 were added from second        document 202, illustrated in FIG. 8. Added elements preserved        their relative order in second document 202.    -   All other graphic elements from first document 201 were        preserved along with any production modified graphic attributes.        As an example, triangular path 520 screen is S2 and rectangular        path 621 clipping path is CP2. Related element associations were        updated to correspond with deleted elements.

FIG. 13 is a diagram illustrating a rendering of exemplary processedmerged document 205. FIG. 14 is a data structure diagram correspondingto FIG. 13 and illustrating aspects of exemplary processed mergeddocument 205 and associated data. Items of note include:

-   -   Trap graphic elements 1303, 1311, 1312, 1322 and 1355 were added        to correspond with new content graphic element boundaries        created by adding graphic elements 802, 810, 830 and 860.        Related element associations for affected graphic elements were        updated.    -   Trap graphic element 1321 clipping path was adjusted to CP2A        because of the boundary created between added rectangular        graphic element 830 and square graphic element 540.    -   Trap graphic elements 665A D were unaffected because the        boundaries between path graphic element 550 and text graphic        element 570 did not change.        Visual Comparison

The method of FIG. 3 also includes steps that allow visual comparison offirst document 201 and second document 202. These steps begin afterdocument comparator 210 has generated edit script 250. In one embodimentof the invention, comparison visualizer 230 begins at block 310 bygenerating three temporary documents based on first document 201, seconddocument 202 and edit script 250. These documents, which can be saved todata store 110 for later use, include:

-   -   Unique to first document 231, includes the graphic elements        existing in first document 201 alone. An exemplary method for        generating document 231 is to select the graphic elements having        “delete” actions in edit script 250.    -   Unique to second document 232, includes the graphic elements        existing in second document 202 alone. An exemplary method for        generating document 232 is to select the graphic elements having        “add” actions in edit script 250.    -   Common to both 233, includes the graphic elements identified as        sufficiently similar in first document 201 and second document        202. An exemplary method for generating document 233 is to        select the graphic elements examined during the comparison and        identified “no action” actions in edit script 250.        According to one embodiment of the invention, production graphic        elements are excluded from the creation of the temporary        documents so that visual comparison of content only graphic        elements is achieved.

Next, in block 312, component visualizer 230 presents a GUI including amulti layered rendering of the temporary documents. The renderings showdefined overprint and knock out characteristics within a layer. Whenmore than one layer is visible, the pixels from each visible layer arecomposited. When composited, graphic element pixels in higher layersknock out graphic element pixels in lower layers so that boundariesbetween objects existing in different layers are more visible. GUIviewing controls are provided to:

-   -   control the visibility of each layer;    -   control the layering order of each rendering;    -   adjust the tonality or color of each layer to distinguish        graphic elements, having similar tone or color, between layers;    -   select one or more graphic elements by asserting graphic element        attribute values (e.g. select path graphic elements), causing        the graphic element to be highlighted in the GUI; and    -   select one or more graphic elements by pointing at an exposed        area of the graphic element's pixels in the GUI, causing the        graphic element to be highlighted in the GUI.

U.S. patent application Ser. No. 10/677,332 entitled “Method ForDisplaying Selected Or Highlighted Objects Using Raster Compositing”describes graphic element GUI compositing and selection methods and ishereby incorporated by reference herein.

FIG. 15 is a diagram illustrating the rendered display portion ofcomponent visualizer 230 GUI from the previously detailed example withall layers visible. Layer common to both 233 is on top, followed byunique to second document 232 and unique to first document 231. Thetonality of unique to second document 232 has been decreased so that itsdark colored pixels now appear as medium colored hatched fills andmedium colored strokes. This view shows the difference in size betweengraphic elements 510 and 810. It also clarifies the boundary betweengraphic element 540 and 830. However, in this view, graphic element 860knocks out graphic element 560.

FIG. 16 is a diagram illustrating the rendered display portion ofcomponent visualizer 230 GUI from the previously detailed example withall layers visible. Layer unique to first document 231 is on top,followed by common to both 233 and unique to second document 232. Thisview shows all of graphic element 510 but obscures graphic element 810.This view also shows the difference in stroke width between graphicelements 560 and 860.

FIG. 17 is a diagram illustrating the rendered display portion ofcomponent visualizer 230 GUI from the previously detailed example withall layers visible. Layer unique to second document 232 is on top,followed by common to both 232 and unique to first document 231. Thislayer presents little new information, relative to the other views, onlybecause of the nature of the particular example. FIG. 17 furtherillustrates the effects of layer knockouts distorting the artist'svisual intent. In another embodiment of the invention, comparisonvisualizer 230 can include another layer containing the rendering ofmerged document 203. This enables the artist's visual intent to beviewed in conjunction with the temporary documents.

Block 314 continues after the initial presentation of the layered viewGUI. In addition to the GUI view controls described above, documentvisualizer 230 provides controls enabling the user to override actionsin the automatically generated edit script 250. Controls are providedto:

-   -   view the properties of a selected graphic element, including an        indication of whether the selected graphic element is present in        merged document 203;    -   delete the selected graphic element from the merged document to        effect an override in edit script 250, wherein:    -   deleting from common to both 232 results in the “no action”        (from first document 201) action being replaced by an add (from        second document 202) action for the graphic element in second        document 202 having the same identifier,    -   deleting from unique to first document 231 results in the delete        (from first document 201) action being replaced by a “no action”        action, and    -   deleting from unique to second document 232 results in the “add”        action being removed; and    -   enable or disable the visibility of deleted graphic element in        its corresponding layer.

Block 314 continues with comparison visualizer 230 updating edit script250 with all action overrides resulting from the GUI session. Block 314completes with comparison visualizer 230 adjusting production graphicelements actions, affected by the action overrides, in edit script 250.For example, a “derived delete” action can be removed if the “delete”action for a related content graphic element is overridden. The methodthen proceeds to block 316, where a decision is made to reapply editscript 250. If edit script 250 has been overridden, the decision can beyes, based on a user preference or in response to a prompt provided fromcomparison visualizer 230 GUI. If the decision is yes, the methodproceeds to block 317, having the same behavior as block 308, and thento block 318. If the decision is no, the method proceeds directly toblock 318.

In another embodiment of the invention, comparison visualizer 230executes a method for viewing, based on a single layered document ratherthan multiple documents. A pre requisite for this method is that eachgraphic element in the document is associated with one view layer.During display of the document, control of a layer's visibilitydetermines whether pixels, corresponding to the graphic elementsassociated with that layer, are displayed. The document defines onedisplay order for all graphic elements amongst all layers. The layereddocument can be produced by document merger 220, comparison visualizer230 or by other means.

The layered document can be produced by selecting graphic elementscategorized as common to both documents (chosen from either document),unique to the first document and unique to the second document. Graphicelements can be associated to a layer corresponding to their category.Graphic elements chosen from the first document retain their relativedisplay ordering. Similarly graphic elements chosen from the seconddocument retain their relative display ordering. Graphic elements chosenfrom one document are also ordered relative to graphic elements, chosenfrom the other document, that are sufficiently similar to graphicelements from the one document. For example, if a first documentcomprises an ordered list of graphic elements: A, B1, and C and a seconddocument comprises an ordered list of graphic elements: D, B2, and E,the layered document can comprise an ordered list of graphic elements:A, D, B1, C, and E. In this example B1 and B2 are sufficiently similar.Other alternate orderings that preserve the relative ordering from bothdocuments are possible (e.g. D, A, B1, E, C).

In some embodiments, document comparator 210, document merger 220 andcomparison visualizer 230 can be adapted to extend the inventive methodsbeyond two documents. As an example, when a document is reproduced in adisplay or in print with content that varies according to a regionalpreference (e.g. language and pricing), several documents can sometimesbe produced. Each document can contain common graphic elements as wellas ones that are unique to a particular regional version. Each documentcan also comprise a composite color document, where graphic elements canpaint in multiple colors, or a color separated document. It is commonpractise to define regionally varying content using fewer colors (e.g.black). Thus, it may be expected that there is no version-specificcontent in certain colors (e.g. cyan, magenta and yellow).

Unfortunately, the manual process of producing these documents cansometimes result in intended common content being somewhat different(e.g. a graphic element accidentally deleted, display order shifted orotherwise modified in one version). So, determining these discrepanciesbefore printing is important. It is desirable to merge these separateversion documents into one layered document so that discrepancies can bemore easily determined through visual means and to simplify theregionalized reproduction process. When merging graphic elementstogether, it is important to classify each one as either common amongstall version documents or unique to one or more version documents. It isalso imporant to preserve a graphic element's display order, relative toother graphic elements from its corresponding version document.

Methods, similar to those described above, can be used to merge a set ofversion documents into a single layered document. Exemplary methods aredescribed below. In summary, layers are identified, based on the versiondocuments. For example, a common layer and one layer corresponding toeach version document can be identified. One document is identified as abase document to construct an initial layered document comprisinggraphic elements assigned to the common layer. Each version document iscompared with the current layered document in sequence to merge theversion document's graphic elements into the layered document andassociate each graphic element with an appropriate layer.

FIG. 18 is a diagram illustrating graphic elements of an exemplary setof composite color version documents according to one embodiment of theinvention. English document 1810 contains common (e.g. graphics andphotos) and english language-specific (e.g. captions and text) content.French document 1820 contains common and french language-specificcontent. US document 1830 contains common and US-specific (e.g. prices)content. Canadian document 1840 contains common and Canadian-specific(e.g. prices) content. Each document is depicted as a display-orderedlist of graphic element identifiers corresponding to graphic elements,determined, for example, by interpreting a document page descriptionlanguage (PDL). For clarity, additional document and graphic elementinformation is not illustrated.

List 1811, for example, includes the graphic element identifiers 1812for English document 1810. Graphic element identifier 1812A has thecharacter value “A”. Other value ranges, such as integers, can be used.Thus, the graphic element corresponding with identifier 1812A displaysfirst, followed by the one associated with identifier 1812B and so on.

A comment 1813 is provided for illustrative purposes beside each graphicelement identifier 1812. It indicates the original intent of theassociated graphic element. For example, the graphic element associatedwith identifier 1812A is intended to be commonly defined amongst allversion documents. “Commonly defined” means that the visual appearanceof the graphic element is substantially the same as presented in eachversion document. That means that it's attributes (e.g. color, geometryand other attirbutes) are sufficiently similar (as described above) andits relative display order is consistent amongst the version documents.Other comment values indicate that the corresponding graphic element'sintent is to provide version-specific content.

For illustrative purposes, inconsistencies have been created in theillustrated version documents. As an example, English document 1810 ismissing common element “G”. As another example, French document 1820 ismissing common element “B”. As another example, graphic elements “E” and“L” have been repositioned in the display order of US document 1830.They should have been positioned after element “D”. As another example,graphic element “Z” was intended to be element “D” but was somehowmodified so that it is not sufficiently similar to the definition in theother documents and is thus identified as a unique element.

FIG. 19 is a diagram illustrating an exemplary method for mergingversion documents into a layered document according to one embodiment ofthe invention. The method begins at block 1902 and proceeds to block1904 where the set of version documents (e.g. 1810, 1820, 1830 and 1840)are obtained by document merger 220. Document merger 220 identifieslayers at block 1906 and associates each layer with a version document.This can be done automatically, by association with version documentnames or other attributes. Alternatively, a user can identify layers andassociate each with a version document. A subset of the versiondocuments can be merged if desired.

Next, the method proceeds to block 1908 where one version document isidentified as the base document (e.g. English document 1810) containingthe candidate common graphic elements. Next, at block 1910, each versiondocument is interpreted to form display-ordered graphic elementrepresentations if the documents were in PDL format.

Next, at block 1912, unique identifiers are established for each graphicelement amongst all the version documents. Methods, similar to thosedescribe above, are used to assign the same identifier to graphicelements in different documents if those graphic elements aresufficiently similar. In some embodiments, this can be optionallypreceded by an adjustment of graphic element attributes based oncharacteristics of the version documents. For example, a trim box orother page-level characteristics can be different in each document,causing similar graphic elements to have different positions.Compensation for this inconsistency can be accomplished, for example, byaligning the centre of trim boxes.

Next, at block 1914, graphic element identifier lists (e.g. 1811, 1821,1831, and 1841) are created with one corresponding to each versiondocument. A base list (e.g. English list 1811) is identified,corresponding to the base document.

Next, at block 1916, an initial version of a merged list is created fromthe base list. A merged list 2001, exemplified by initial merged list2001A in FIG. 20, comprises a display-ordered list of graphic elementidentifiers 2002 with associated layer identifiers 2003. In thisexample, initial merged list 2001A includes each graphic elementidentifier from list 1811 with each identifier assigned to layer 0. Inthis example, 0 is the value representing the “common” layer, 1 is thevalue representing “unique to English document” layer, 2 is the valuerepresenting the “unique to French document” layer, 3 is the valuerepresenting the “unique to US document” layer, and 4 is the identifierrepresenting the “unique to Canadian document” layer.

Next, at block 1918, document merger 220 determines if another versiondocument exists. If not, it proceeds to block 1928. If yes, it proceedsto block 1920 to begin the process of merging this version document.

Proceeding at block 1920 the version document is established as thecurrent version document and at block 1922 the corresponding list isestablished as the current list to be merged. Thus, for example, Frenchdocument 1820 and French list 1821 are first identified as current.

Next, document merger 220 proceeds to block 1924 where it provides afirst list, comprising only element identifiers derived from merged list2001 to document comparator 210. Document comparator 210 also receives asecond list, derived from the current list in order to generate datasuitable for updating merged list 2001. As an example, for the firstiteration, merge list 2001A and French list 1821 are used to derive thefirst and second lists, respectively. Document comparator 210 generatesedit script 250 as a result for document merger 220.

Next, at block 1926, document merger 220 applies edit script 250 tomerged list 2001 in conjunction with the version document lists to forman updated merged list 2001. An example of this is described in detailbelow. Next, document merger 220 proceeds to block 1918 as describedabove.

Proceeding at block 1928, document merger 220 has determined that noadditional version document lists need to be merged into merged list2001. Document merger 220 produces layered merged document 203 frommerged list 2001. Each graphic element in merged document 203 isassociated with the layer identified in merged list 2001. Mergeddocument 203 can be represented in display-ordered list form oroptionally in PDL format. Upon creating layered, merged document 203,the method completes at block 1930.

FIG. 20 is a diagram illustrating intermediate results of an exemplaryversion document merging method according to one embodiment of theinvention. The intermediate results of the method of FIG. 19 aredepicted as a series of rounds 2010, 2020, 2030 and 2040. As describedabove, first round 2010 depicts initial merged list 2001A.

Second round 2020, corresponding to results from merging French list1822 with merged list 2001A, depicts summary data for first list 201A,second list 202A, and edit script 250A.

Lists 201 and 202 are depicted, with staggered entries for illustrativepurposes only, so that each graphic element identifier is associatedwith only one action from edit script 250. Actions depicted as “=”correspond to a “no action” action, indicating that the associatedelement identifier is common to both lists 201 and 202. Actions depictedas “−” correspond to a “delete” action, indicating that the associatedelement identifier is unique to first list 201. Actions depicted as “+”are an “add” action, indicating that the associated element identifieris unique to second list 202.

For second round 2020, first list 201A comprises a display-ordered listof graphic element identifiers selected from merged list 2001A. Thecriteria for selection is graphic elements associated with the (common)layer 0. In this case, that is all of the graphic elements, indicatingthat all are still candidates to be common graphic elements.

For second round 2020, second list 202A comprises a display-ordered listof graphic element identifers selected from French list 1822. Thecriteria for selection can be established to include the entire list, asdepicted in these examples. In some embodiments it may be preferred tofirst examine French list 1822 to determine if there are any graphicelement identifers that are not in the set of those already associatedwith layer 0 of merged list 2001A. This may be done, for example, toreduce the number of comparisons performed by document comparator 210.In this case, graphic element identifiers, corresponding to those thatare not selected, can be modified to flag them for subsequentprocessing, described below. For example, if integer identifiers areused, an element identifer can be negated to indicate that it wasn'tcompared by document comparator 210 and thus is not referenced by editscript 250.

Second round 2020 also depicts an updated merged list 2001B generated byapplying edit script 250A. The method for applying edit script 250 ofthe examples of FIG. 20 is described in the following. Actions from editscript 250 are processed in order.

A graphic element identifier associated with an “=” action is leftuntouched in merged list 2001 since they it is still a candidate commongraphic element. A graphic element identifier associated with a “+”action is added to merged list 2001. It is assigned a layer identifiercorresponding to the layer associated with the current version list anddocument. A graphic element identifier associated with a “−” actionremains in merged list 2001. However, its layer assignment is modifiedfrom layer 0, since they it is no longer a common candidate. Additionalcopies of the reclassified graphic element identifier may also need tobe added to merged list 2001 as described below.

Referring to second round 2020, one can see that graphic elementidentifiers “A”, “D”, “E”, and “H” have been identified by edit script250A as common. Thus, their entries in merged list 2001B remainunchanged.

Graphic element identifiers “B”, “C”, and “F”, have been identified asunique to first list 201A. Thus, their entries in merged list 2001B arechanged to reflect that they are unique to (English) layer 1.

Graphic element identifiers ““I, “J”, and “G” have been identified asunique to second list 202A. Thus, entries for these graphic elements areadded in merged list 2001B. They are added, with their relative orderpreserved, before the next element identifier that is commonly definedby first list 201A and second list 202A (e.g. “D” and “H”). The addedentries are assigned (French) layer 2. As indicated above, in someembodiments, these graphic element identifiers would not have beencompared. In this case, as each “=” action is processed, document merger220 can examine the list used to derive second list 202 for negatedelement identifiers preceding a common graphic element. These elementidentifiers can be added to merged list 2001 before the associatedcommon graphic element identifier while preserving their relative orderfrom their originating list.

Referring to third round 2030, the method produces similar results withfirst list 201B derived from merged list 2001B, second list 202B derivedfrom US list 1832 and corresponding edit script 250B. Merged list 2001Cis produced with the following new aspects illustrated. Graphic elementidentifier “D” has been identified as unique to first list 201B. Since201B corresponds to previously merged English list 1812 and French list1822, entries corresponding to each list must now appear in merged list2001C. Accordingly, the existing entry's layer association is modifiedto correspond with (English) layer 1. Another entry, corresponding toFrench list 1822, is added with a (French) layer 2 association after thelayer 1 entry and before the common entry (e.g. “E”).

It is noteworthy that the method has determined that “E” is commonamongst the first three version documents, even though its relativeorder is different in US list 1832. This is an anomaly of the methodthat will still result in the inconsitency being determined upon visualinspection of layered merged document 203. That is, element “D” will beidentified as unique to each version document which upon closerinspection of graphic element attributes will lead to the identificationof the discrepancy with “E”.

Referring to fourth round 2040, the final version of merged list 2001Dis illustrated, indicating common graphic element identifiers andversion-specific graphic element identifiers associated with theappropriate layer.

Other aspects of merging version documents can optionally be present inother embodiments. One aspect includes altering graphic element colorantvalues during creation of merged document 203 to provide unique colorantnames amongst the layers. As an example, graphic elements that paintblack can be renamed “Common black” for the common layer, “Englishblack” for the English layer, and so on. This can enable more granularcolor separation control.

Another aspect includes identifying a list of expected colorants paintedby graphic elements associated with a layer. This can facilitate forexample, automatic detection of discrepancies. As an example, a graphicelement painting an unexpected color for its associated layer can beassociated with an “error” layer to enable quicker visual analysis.

Another aspect includes identifying whether a graphic element associatedwith a version-specific layer of the layered merged document 203 hascharacteristics that will knock out a portion of a graphic elementassociated with the common layer. Problems can arise where some whereversion content is typically defined to paint in only a few colors (e.g.black). This means that all of the cyan, magenta and yellow plates willbe common amongst each printed version and can be reused for each printjob. Inconsistencies in the common plates can be overlooked by visuallyinspecting a layered document when rendering a layered document withselected layers enabled.

As an example of a problem that can occur, assume two version-specificgraphic elements, each painting black colorant with a knock out settingenabled where each is defined by a different version document and eachhave different but overlapping geometries and where each paints after acommon graphic element that paints cyan. When rendered with common andany one of the version-specific layers enabled, the version-specificgraphic element knocks out (e.g. creates an absence of color) in thecyan plane of the rendered image so that pixels corresponding to thegraphic element only paint black. Note that each knocks out a differentset of pixels because of their different geometries. If only the commonlayer is enabled, the knock out does not occur since theversion-specific graphic element was not rendered. Thus, if only thecommon layer is enabled, cyan pixels corresponding to the common graphicelement are painted in the region where the version-specifc elementswould have painted if rendered.

Thus, when visually inspecting a layered document, in a display forexample, using layer-enabling controls, one can falsely conclude thatthe common colorants painted by the common layer are correct since thepixels for the common colorants are being rendered each time the layercontrols are changed. When printing however, if the common plates (e.g.cyan) are generated while rendering a specific version of the document,the cyan plate will contain the white knock out corresponding to theversion-speicifc graphic element. Thus the cyan plate will not becommon, and this may not be discovered at an opportune time.

To address this visual inspection anomaly, some embodiments can identifygraphic elements, associated with a version-specific layer, having aknock out characteristic. Once such a version-specific graphic elementhas been identified, an identically shaped knock out graphic element canbe added to the layered document to paint before the version-specificgraphic element. The knock out graphic element is defined to paint white(e.g. no colorant) in each of the expected colorants of the commonlayer. The knock out graphic element is associated with both the commonlayer and the layer associated with the version-specific graphicelement. Thus, when visually inspecting the layered document with eitherthe common or version-specific layers, the white knock out graphicelement will be observed. In the specific example from above with onlythe common layer enabled, one would see the effects of both knock outgraphic elements and could recognize that a cyan plate would not becommon.

As an alternative embodiment, each combination of the common layer andone version-specific layer can be rendered to produce the raster for theexpected common color planes. The raster for each color plane can thenbe compared pixel-wise to automatically determine if there are anydifferences. Locating any differences that exist may also be quickergiven the ability to highlight pixel areas where differences occur.

Another aspect includes merging an updated version document (e.g. withcorrections) into an existing layered document. This can be accomplishedby eliminating entries from existing merged list 2001 that correspond tothe layer associated with the version document to be replaced. Mergingis accomplished by merging the updated version document in a new round,recognizing which rounds that have previously been performed.

In another aspect, a layered merged document 203 can be reproduced withmultiple layers enabled to produce a desired version of the document.For example, common, English, and US layers can be enabled to reproducea version suitable for an english-speaking US audience.

Layer based adjustment of tonality and color may not be provided in someembodiments. In these cases, the ability to distinguish graphic elementborders can be accomplished by controlling layer visibility andselecting graphic elements, causing their colors or fills to be altered.

Certain implementations of the invention comprise computer processors,which execute software instructions, which cause the processors toperform a method of the invention. For example, document comparator 210,document merger 220, comparison visualizer 230 and additional processing240 can all be implemented by providing software, which runs on, or morecomputer systems 100 and causes the computer systems to operateaccording to the methods described above. The program product maycomprise any medium which carries a set of computer readable signalscomprising instructions which, when executed by a computer processor,cause the computer processor to execute a method of the invention. Theprogram product may be in any of a wide variety of forms. The programproduct may comprise, for example, physical media such as magneticstorage media including floppy diskettes, hard disk drives, optical datastorage media including CD ROMs, DVDs, electronic data storage mediaincluding ROMs, flash RAM, or the like or transmission type media suchas digital or analog communication links. The instructions mayoptionally be compressed and/or encrypted on the medium.

The foregoing descriptions have detailed comparison of documents,primarily in the context of a production environment. It is understoodthat the methods of the invention have applicability beyond thosedescribed. Examples of adapting the basic methods through differentembodiments include using a subset of the methods, using alternatearchitectures, selection criteria and rule sets.

The scope of the invention is to be construed in accordance with thesubstance defined by the following claims. As will be apparent to thoseskilled in the art in the light of the foregoing disclosure, manyalterations and modifications are possible in the practice of thisinvention without departing from the spirit or scope thereof. Forexample, certain modifications, permutations, additions andsub-combinations of the features described herein will be apparent tothose skilled in the art. It is intended that the following appendedclaims and claims hereafter introduced should be interpreted broadly soas to encompass all such modifications, permutations, additions andsub-combinations as are consistent with the language of the claims,broadly construed.

1. A method for comparing a plurality of documents, the methodcomprising: obtaining a plurality of documents each comprising aplurality of graphic elements; and associating a plurality of uniqueelement identifiers with the graphic elements of the plurality ofdocuments wherein, upon determining that a first graphic element of afirst document is sufficiently similar to a second graphic element of asecond document, the method comprises associating the same uniqueelement identifier with both the first graphic element and the secondgraphic element.
 2. A method according to claim 1 wherein comparing aplurality of documents also includes organizing the plurality of uniqueelement identifiers into a plurality of lists corresponding to theplurality of documents wherein entries in a list correspond to a displayorder of graphic elements of a document.
 3. A method according to claim2 wherein the plurality of documents comprises a plurality of versiondocuments wherein a version document represents one version of adocument.
 4. A method according to claim 3 comprising merging aplurality of version documents into a layered document.
 5. A methodaccording to claim 4 wherein merging the plurality of version documentsinto a layered document comprises: identifying a plurality of layers forthe layered document; creating a plurality of list associations whereineach list association comprises an association between a layer and alist of the plurality of lists; adding a plurality of merged elements toa merged list wherein each merged element comprises an elementidentifier of the plurality of unique element identifiers and anassociation with at least one layer of the plurality of layers; andgenerating a layered document based on the merged list and the pluralityof version documents.
 6. A method according to claim 5 whereinidentifying the plurality of layers includes identifying a common layerand at least one version-specific layer.
 7. A method according to claim6 wherein identifying at least one version-specific layer comprisesidentifying a layer for each version document.
 8. A method according toclaim 6 wherein creating the plurality of list associations comprisescreating associations for the at least one version-specific layer.
 9. Amethod according to claim 8 wherein merging the plurality of versiondocuments into a layered document includes identifying one of theplurality of documents as a base document and identifying a base list asthe list corresponding to the base document.
 10. A method according toclaim 9 wherein adding the plurality of merged elements to a merged listcomprises first adding a plurality of merged elements with elementidentifiers corresponding to the base list, and with an order therefrom,and wherein each merged element identifier is associated with the commonlayer.
 11. A method according to claim 10 wherein adding the pluralityof merged elements to a merged list also includes: determining at leastone list that remains unexamined from the plurality of lists; andupdating the merged list based on the at least one list that remainsunexamined.
 12. A method according to claim 11 wherein updating themerged list based on the at least one list that remains unexaminedcomprises: selecting a list, from the at least one list that remainsunexamined, as the current list to be examined; deriving a first listbased on the current merged list; deriving a second list based on thecurrent list; deriving edit data from the first and second lists whereinthe edit data can be used to change the first list into the second list;applying the edit data to the current merged list to produce an updatedmerged list wherein applying is done in conjunction with the pluralityof lists and the plurality of list associations; and repeating the abovesteps if there is an unexamined list remaining.
 13. A method accordingto claim 12 wherein deriving a first list based on the current mergedlist comprises deriving the first list by selecting, in order, elementidentifiers associated with the common layer.
 14. A method according toclaim 12 wherein the edit data comprises a plurality of actions whereinactions comprise actions of a plurality of action types, the actiontypes including: delete, corresponding to an element identifier that isunique to the first list; add, corresponding to an element identifierthat is unique to the second list; and no action, corresponding to anelement identifier in the first list that is sufficiently similar to anelement identifier in the second list.
 15. A method according to claim14 wherein deriving the edit data from the first and second listscomprises: examining identifiers from the first and second lists in anordered fashion until a current common identifier is found; creating ano action action in the edit data for the current common identifier;creating delete actions in the edit data for all identifiers in thefirst list between the previous common identifier, or the start of thefirst list initially, and the current common identifier; creating addactions in the edit data for all identifiers from the second list,occurring between the previous common identifier, or the start of thesecond list initially, and the current common identifier; and repeatingthe steps above until the end of the first and second lists is reachedwherein the end of the first and second lists are treated as a currentcommon identifier for the creating delete actions and creating addactions steps.
 16. A method according to claim 15 wherein deriving editdata from the first and second lists comprises using a largest commonsubstring algorithm.
 17. A method according to claim 14 wherein applyingthe edit data to the current merged list to produce an updated mergedlist comprises: changing a layer associated with a merged elementidentifier if the element identifier is associated with a delete actionin the edit data; and adding a merged element for an element identifierassociated with an add action in the edit data.
 18. A method accordingto claim 17 wherein changing the layer associated with a merged elementidentifier comprises changing the associated layer from the common layerto the layer associated with the base list.
 19. A method according toclaim 18 wherein changing the layer associated with a merged elementidentifier also includes adding a merged element for each previouslyexamined list, excluding the base list and the current list.
 20. Amethod according to claim 19 wherein adding the merged element for eachpreviously examined list comprises, for each previously examined list:adding the merged element with a position after the merged elementassociated with the delete action and before the next merged elementassociated with the common layer; assigning an element identifiercorresponding to the element identifier associated with the deleteaction; and associating the element identifier with the layer associatedwith the previously examined list.
 21. A method according to claim 17wherein adding the merged element for an element identifier associatedwith an add action in the edit data comprises: associating the mergedelement identifier with a layer corresponding to the layer associatedwith the current list; and positioning the merged element to preserve arelative element identifier order from the current list amongst aplurality of merged elements corresponding to element identifiers fromthe current list.
 22. A method according to claim 12 wherein derivingthe second list based on the current list comprises selecting thecurrent list as the second list.
 23. A method according to claim 12wherein deriving the second list based on the current list comprisesexamining the current list in an element-wise order wherein examining acurrent list element comprises: determining whether the elementidentifier exists in a current merged list element with an associationto the common layer; adding the element identifier to the second list ifdetermining yields a positive result; and altering the elementidentifier in the current list if determining yields a negative result.24. A method according to claim 23 wherein altering the elementidentifier in the current list comprises altering the element identifierto indicate that it is a version-specific element identifier whilepreserving its graphic element identifying characteristic.
 25. A methodaccording to claim 24 wherein altering the element identifier comprisesnegating the element identifier.
 26. A method according to claim 24applying the edit data to the current merged list to produce an updatedmerged list also includes adding a merged element for an altered elementidentifier of the current list.
 27. A method according to claim 26wherein adding the merged element for an altered element identifier ofthe current list comprises: adding the merged element with an elementidentifier corresponding to the altered element identifier; associatingthe merged element identifier with a layer corresponding to the layerassociated with the current list; and positioning the merged element topreserve a relative element identifier order from the current listamongst a plurality of merged elements corresponding to elementidentifiers from the current list.
 28. A method according to claim 6wherein generating the layered document comprises generating a pluralityof layered graphic elements with an order corresponding to the order ofentries of the merged list and wherein a layered graphic elementcorresponds to an element identifier of the merged element and wherein alayered graphic element is associated with at least one layer associatedwith the merged element identifier.
 29. A method according to claim 28wherein generating a layered document also includes reproducing thelayered document.
 30. A method according to claim 29 wherein reproducingthe layered document includes reproducing in a display or reproducing inprint.
 31. A method according to claim 29 wherein reproducing thelayered document comprises: selecting at least one layer to bereproduced; selecting, in order, at least one graphic element of thelayered document wherein a graphic element is selected if it isassociated with a the at least one layer to be reproduced; andreproducing the at least one graphic element by painting the at leastone graphic element in order.
 32. A method according to claim 28 whereinidentifying the plurality of layers for the layered document alsoincludes identifying, for a layer, a set of expected colorants to bepainted by graphic elements associated with the layer.
 33. A methodaccording to claim 32 wherein generating a layered document includesidentifying a graphic element associated with a layer if the graphicelement paints a colorant other than one included in the set of expectedcolorants identified for the layer.
 34. A method according to claim 33wherein identifying the graphic element also includes associating thegraphic element with an error layer.
 35. A method according to claim 32wherein generating the plurality of layered graphic elements alsoincludes automatically identifying a difference between a first andsecond raster produced for an expected common colorant from a firstreproduced version and a second reproduced version, respectively.
 36. Amethod according to claim 35 wherein the first reproduced versioncomprises a raster reproduction of the layered document based on a firstselection of layers wherein the first selection includes the commonlayer; the second reproduced version comprises a raster reproduction ofthe layered document based on a second selection of layers wherein thesecond selection includes the common layer and wherein the firstselection and second selection of layers are different; the expectedcommon colorant is based on the set of expected colorants to be paintedby graphic elements associated with the common layer; and automaticallyidentifyng a difference between the first and second raster comprisesperforming a pixel-wise comparison of the first and second raster toidentify a pixel that differs between the first and second raster.
 37. Amethod according to claim 32 wherein generating the plurality of layeredgraphic elements also includes identifying a first and second layeredgraphic element of the plurality of layered graphic elements wherein thefirst layered graphic element is associated with a version-specificlayer and has a knock out characteristic and paints on top of at least aportion of the second layered graphic element wherein the second layeredgraphic element is associated with the common layer.
 38. A methodaccording to claim 37 wherein identifying the first and second layeredgraphic element also includes adding a knock out layered graphic elementto the layered document wherein the knock out layered graphic elementpaints an absence of colorant in each of the set of expected colorantsto be painted by graphic elements associated with the common layer. 39.A method according to claim 38 wherein adding the knock out layeredgraphic element comprises: adding the knock out layered graphic elementto paint an area corresponding to an area painted by the first layeredgraphic element; positioning the knock out graphic element to paintbefore the first layered graphic element and after the second layeredgraphic element; and associating the knock out graphic element with boththe common layer and the layer associated with the first layered graphicelement.
 40. A method according to claim 5 wherein identifying theplurality of layers for the layered document also includes identifying aplurality of color mappings for the plurality of layers wherein a colormapping for a layer defines a substitute colorant for at least oneoriginal colorant painted by a graphic element associated with thelayer.
 41. A method according to claim 12 wherein merging the pluralityof version documents into a layered document comprises merging anupdated version document into the merged list and regenerating thelayered document.
 42. A method according to claim 41 wherein merging theupdated version document into the merged list comprises: first ensuringthat the updated version document is for updating an original versiondocument other than the base document; secondly ensuring a layerassociated with the original version document comprises a layerassociated with only one version document; deleting a merged elementfrom the merged list if the merged element is associated with the layer;associating a plurality of unique element identifiers to the graphicelements of the updated version document based upon an originalplurality of unique element identifiers corresponding to the pluralityof version documents; organizing the plurality of unique elementidentifiers corresponding to the updated version document into anupdated list wherein entries in the updated list corresponds to adisplay order of graphic elements of the updated version document;adding the updated list to the at least one list that remainsunexamined; and updating the merged list based on the at least one listthat remains unexamined.
 43. A method according to claim 9 whereinassociating a plurality of unique element identifiers to the graphicelements of the plurality of documents comprises: associating a uniqueelement identifier with each graphic element of a first plurality ofgraphic elements of a first document of the plurality of documents;determining a second plurality of graphic elements by combining theplurality of graphic elements of the remaining plurality of documents;comparing each one of the second plurality of graphic elements with thefirst plurality of graphic elements; associating a unique elementidentifier with a graphic element of the second plurality of graphicelements if the graphic element is not sufficiently similar to anygraphic element of the first plurality of graphic elements; and,associating an existing element identifier with the graphic element ofthe second plurality of graphic elements if the graphic element issufficiently similar to the first graphic element of the first pluralityof graphic elements wherein the first graphic element is associated withthe existing element identifier.
 44. A method according to claim 43wherein the first document is the base document.
 45. A method accordingto claim 44 wherein comparing each one of the second plurality ofgraphic elements with the first plurality of graphic elements comprisesperforming a plurality of element wise comparisons based on a pluralityof similarity rules.
 46. A method according to claim 45 whereincomparing each one of the second plurality of graphic elements with thefirst plurality of graphic elements comprises also includes firstadjusting the second plurality of graphic elements based oncharacteristics of the plurality of version documents.
 47. A methodaccording to claim 46 wherein adjusting the second plurality of graphicelements based on characteristics of the plurality of version documentscomprises aligning a centre of a plurality of trim boxes correspondingto the plurality of version documents.
 48. A method according to claim45 wherein performing a plurality of element wise comparisons comprises:creating a hash value for a graphic element based on attribute values ofthe graphic element; associating the graphic element with the hashvalue; and performing an element wise comparison between a first graphicelement and a second graphic element if the first and second graphicelements are associated with the same hash value.
 49. A method accordingto claim 45 wherein the plurality of similarity rules include rules thatidentify two graphic elements as being sufficiently similar if anydifferences in their corresponding attribute values result in the twographic elements being visually similar when reproduced.
 50. A methodaccording to claim 49 wherein a similarity rule is based on at least onegraphic element attribute accuracy value wherein two graphic elementsare considered sufficiently similar if, for each at least one graphicelement attribute accuracy value, the corresponding values of the twographic element attributes differ by less than the correspondingaccuracy value.
 51. A system for comparing a plurality of documents, thesystem comprising: means for obtaining a plurality of documents, each ofthe documents comprising a plurality of graphic elements; and means forassociating a plurality of unique element identifiers with the graphicelements of the plurality of documents wherein, upon determining that afirst graphic element of a first document is sufficiently similar to asecond graphic element of a second document, the method comprisesassociating the same unique element identifier with both the firstgraphic element and the second graphic element.
 52. A system accordingto claim 51 wherein the system for comparing a plurality of documentsalso includes means for organizing the plurality of unique elementidentifiers into a plurality of lists corresponding to the plurality ofdocuments wherein entries in a list correspond to a display order ofgraphic elements of a document.
 53. A system according to claim 52wherein the plurality of documents comprises a plurality of versiondocuments wherein a version document represents one version of adocument.
 54. A system according to claim 53 wherein the system forcomparing a plurality of documents also comprises means for merging aplurality of version documents into a layered document.
 55. A systemaccording to claim 54 wherein means for merging the plurality of versiondocuments into a layered document comprises: means for identifying aplurality of layers for the layered document; means for creating aplurality of list associations wherein a list association comprises anassociation between a layer and a of the plurality of lists; means foradding a plurality of merged elements to a merged list wherein a mergedelement comprises an element identifier of the plurality of uniqueelement identifiers and an association with at least one layer of theplurality of layers; and means for generating a layered document basedon the merged list and the plurality of version documents.
 56. A systemaccording to claim 55 wherein the means for identifying the plurality oflayers includes means for identifying a common layer and at least oneversion-specific layer.
 57. A system according to claim 56 wherein themeans for identifying at least one version-specific layer comprisesmeans for identifying a layer for each version document.
 58. A systemaccording to claim 56 wherein the means for creating the plurality oflist associations comprises means for creating associations for the atleast one version-specific layer.
 59. A system according to claim 58wherein the means for merging the plurality of version documents into alayered document includes means for identifying one of the plurality ofdocuments as a base document and means for identifying a base list asthe list corresponding to the base document.
 60. A system according toclaim 59 wherein the means for adding the plurality of merged elementsto a merged list comprises means for first adding a plurality of mergedelements with element identifiers corresponding to the base list, andwith an order therefrom, and wherein each merged element identifier isassociated with the common layer.
 61. A system according to claim 60wherein the means for adding the plurality of merged elements to amerged list also includes: means for determining at least one list thatremains unexamined from the plurality of lists; and means for updatingthe merged list based on the at least one list that remains unexamined.62. A system according to claim 61 wherein the means for updating themerged list based on the at least one list that remains unexaminedcomprises: means for selecting a list, from the at least one list thatremains unexamined, as the current list to be examined; means forderiving a first list based on the current merged list; means forderiving a second list based on the current list; means for derivingedit data from the first and second lists wherein the edit data can beused to change the first list into the second list; means for applyingthe edit data to the current merged list to produce an updated mergedlist wherein applying is done in conjunction with the plurality of listsand the plurality of list associations, to produce an updated mergedlist; and means for repeating the above steps if there is an unexaminedlist remaining.
 63. A system according to claim 56 wherein the means forgenerating the layered document comprises means for generating aplurality of layered graphic elements with an order corresponding to theorder of entries of the merged list and wherein a layered graphicelement corresponds to an element identifier of the merged element andwherein a layered graphic element is associated with at least one layerassociated with the merged element identifier.
 64. A system according toclaim 63 wherein the means for generating a layered document alsoincludes means reproducing the layered document.
 65. A system accordingto claim 64 wherein the means for reproducing the layered documentincludes means for reproducing in a display or reproducing in print. 66.A system according to claim 64 wherein the means for reproducing thelayered document comprises: means for selecting at least one layer to bereproduced; means for selecting, in order, at least one graphic elementof the layered document wherein a graphic element is selected if it isassociated with a the at least one layer to be reproduced; and means forreproducing the at least one graphic element by painting the at leastone graphic element in order.
 67. A medium carrying a set of computerreadable signals comprising instructions which, when executed by a dataprocessor, cause the data processor to execute a method according toclaim 1.